Project Summary/Abstract Acute myocardial infarction (MI) is complicated by the subsequent development of scar tissue leading to chronic cardiac insufficiency. Unfortunately, the lack of treatments for this maladaptive fibrotic response often leads to a poor prognosis. Early attempts at stem cell delivery and biological therapeutics to address this problem have been promising, but inconsistent. To meet this challenge, the Desai lab, with collaborators, has developed a unique system of randomly dispersed polymeric microstructures, termed microrods, that have been found to decrease fibroblast proliferation and promote cardiomyocyte hypertrophy in vitro. The objective of this proposal is to study the mechanisms of interaction between microrods and cardiac fibroblasts in vitro and in an animal models of infarct. We will also examine the effect of microstructures on cardiac remodeling. This will enable the design of more effective therapies to prevent the development of cardiac scar tissue and encourage recovery of heart function after MI. Based on previous studies and recent research on the mechanical microenvironment, it is hypothesized that primary adult ventricular fibroblasts will respond to the presence of microrods with a unique set of transcriptional changes in pathways relevant to mechanotransduction, micro-environmental interaction, and extracellular matrix (ECM) deposition. In Aim 1, quantitative analyses of changes in gene expression and immunofluorescence microscopy will be used to examine cellular interactions with microrods in 3D culture. Specifically, quantification of ECM down-regulation and mechanotransductive interactions will elucidate the mechanisms of effect of microstructures on fibroblasts. In addition, HepIII conjugated microrods will be developed in order to augment vascularization, another key element of cardiac regeneration. Aim 2 will use quantitative biochemical and immunohistochemical techniques in an established rat model of MI to test the hypothesis that microrod injection into the infarct zone will produce similar transcriptional changes in markers of the fibrotic response as seen in vitro through interaction with the cardiac fibroblast population, as well as angiogenesis produced with the addition of HepIII to the microrods. Finally, Aim 3 will evaluate the therapeutic benefit of injected microrods in the setting of chronic ischemic cardiomyopathy as suggested by preliminary in vivo results. Therapeutic effect after microrod injection will be measured by serial echocardiograms to assess ejection fraction and cardiac anatomy in relation to the infarct scar and angiogenesis. By decreasing fibrotic scarring, inducing angiogenesis and promoting myocardial regeneration, injectable microrods will contribute to improving outcomes after MI. Understanding these mechanisms will lead to the design and optimization of complementary therapies and drug delivery possibilities, which will further the NHLBI's mission of treating heart disease to enhance the health of all individuals so that they can live longer and more fulfilling lives.